[erlang-questions] Mock Functions
Wed Sep 6 09:04:40 CEST 2006
Arnaud Bailly wrote:
> I am implementing a small web application to handle billing of
See my paper from ICFP 2004 at http://www.duomark.com/erlang/ entitled
"Structured Programming Using Processes
I describe implementing a Quicken-like application. Processes are used
in ways that make the code more structured and easier to do things like
swap out the backend storage or frontend presentations. The use of
processes is counter to the typical advice of "one process per real
world activity", but I give historical background on how one decides to
subdivide a system and then argue why processes afford a new approach to
For the past couple years I've been pondering the currently accepted
state-of-the-art in data structures and code organization. The premise
is, "Given processes are as cheap as structures or objects, would you
design things differently?". This year I will present an alternative
approach for implementing traditional data caches.
It seems that a lot of CS decisions were made in the 60s, like
databases, structured programming, code sharing, concurrency, etc. The
world has changed to where memory is cheap and storage is very fast and
potentially endless for most problems. I believe alternate approaches
are effective now to fundamental tradeoffs made when the costs were very
different. The 2004 paper was my first attempt at articulating that
I am working on a library that would clean up parts of the code from the
2004 paper dramatically. With luck it will be available in a couple months.
> How do I mock out something?
It is not even necessary for you to use processes. Put your swappable
functions in a module. Write a replacement module with all the same
signatures. Pass the module name to an initialization function that
launches a process containing the modules you want to assemble for your
system test or deployment.
Think of mocked API as the "-behaviour" as you would specify in a
gen_server implementation module.
Mocking is still useful when you want to simulate time delays (e.g., to
query a terabyte document index) and other external things that affect
the code performance or to model an environment that you cannot
reproduce on your test machines.
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